In pulsed discharge machining, a machining voltage is applied between an electrode of an electric-discharge machining apparatus and a workpiece for machining the workpiece, and the workpiece is machined by a pulsed discharge energy generated during application of the voltage.
In the discharge machining on the workpiece performed by the electric-discharge machining apparatus, a machining accuracy and a removal amount for the workpiece change according to an electrode state and the like. It is, therefore, necessary to accurately detect the electrode state and the like so as to ensure an accurate machining before machining the workpiece.
To accurately machine the workpiece, there is known a technique for calculating a machining amount for the workpiece on the assumption that a discharge machining amount by one effective discharge pulse is constant, and for controlling machining on the workpiece based on the calculated machining amount.
A three-dimensional electric-discharge machining apparatus disclosed in Japanese Patent Application Laid-Open No. H5-345229 includes a counter circuit that detects pulsed discharges during a machining and that accumulates the detected discharges, and a signal converter circuit that converts a machining depth signal into a number-of-pulses signal corresponding to an energy set to a machining power supply according to a machined shape at a machining position on an XY plane. When the detected discharges counted by the counter circuit matches the number of pulses indicated by the signal obtained by the signal converter circuit, a servo-feeding of a servo head to which a pipe electrode is fixed is stopped.
Furthermore, to effectively machine the workpiece, there is known a technique for discriminating discharge pulses that effectively contribute to the machining from discharge pulses that does not effectively contribute to the machining, and for controlling the machining on the workpiece based on the number of discharge pulses effective for the machining.
An electric-discharge machining apparatus disclosed in Japanese Patent Application Laid-Open No. H5-293714 rectifies at least one alternating-current (AC) component or high frequency component among a current, a voltage, and an impedance in a machining gap, smoothes the rectified component, and thereby detecting a discharge state.
However, the removal amount for the workpiece by one effective discharge pulse differs according to a machining surface condition of an electrode for machining the workpiece, a change in a facing area of the electrode relative to the workpiece, a discharge pulse state, and the like. As a result, when the discharge machining amount is detected on the assumption that the discharge machining amount by one effective discharge pulse is constant as disclosed in the conventional techniques, an accurate electric discharge amount cannot be detected. Since the machining processing is controlled on the assumption that the removal amount for the workpiece by one effective discharge pulse is constant, the conventional techniques have a disadvantage in that an error occurs to the machining amount for the workpiece.
The present invention has been achieved in view of the conventional disadvantages. It is therefore an object of the present invention to provide an electric-discharge machining apparatus that corrects a removal amount for a workpiece set for performing a discharge machining according to an electrode state and the like, and that controls a machining processing on the workpiece based on the corrected removal amount.